Radar apparatus with quiet switch calibration and associated methods

ABSTRACT

A radar apparatus measures at least one characteristic of at least one object. A sweep generator generates a sweep signal to modulate an oscillator to generate a varying frequency signal. A transmitter transmits the varying frequency signal as a radar signal. A receiver receives a reflected radar signal to produce a received signal using the varying frequency signal. A compensation signal memory holds a previously stored compensation signal. A compensation circuit compensates the received signal based on the previously stored compensation signal to produce a compensated received signal. A quiet switch quiets the reflected radar signal and determines the previously stored compensation signal, during calibration of the radar apparatus, and the received signal is written into the compensation signal memory. Switched loads can be used to quiet the reflected radar signal. For field calibration, the compensated signal can be adjusted but not necessarily written back into the compensation signal memory.

BACKGROUND OF THE INVENTIONS

1. Technical Field

The present inventions relate to radar systems which measurecharacteristics of detected objects and, more particularly, relate tocalibrated radar systems useful for at least applications which measurecharacteristics of detected objects with quiet switch calibration.

2. Description of the Related Art

Radar systems have been used for distance ranging and speeddetermination. Frequency Modulated Continuous Wave (FMCW) is one commonform of radar signaling. Accuracy of determinations of speed or distanceranging has been improved using calibration.

One traditional way for detection of targets with a radar system is totransmit a carrier signal of a known strength and frequency, which thenreflects off the target of interest, and then the signal is received bythe radar unit. This received signal is then mixed with the transmittedsignal, and any frequency difference between the two signals (the“mixing product”) results in what is known as a “beat note”, which is alow-frequency signal (often less than 1000 Hz) which represents theinstantaneous difference of the frequencies being transmitted andreceived. The farther away the target, the greater the frequencydifference, which results in a higher frequency beat note. Thissignaling method used for these systems is called: frequency modulatedcontinuous wave (FMCW).

For typical open-air applications (such as vehicle collision avoidance,presence detection for security or lighting control, and automatic dooropening), the FCC limits the range of frequencies allowed. For example,in the 24 GHz band, the limits are 100 MHz or 250 MHz depending on theapplication. This band limit, in turn, limits how high in frequency abeat note can be effectively generated for a target at a given range.

In traditional FMCW radar systems, the detection and measurement oftargets is done by analyzing the beat note with a Fast Fourier Transform(FFT), which provides a means of directly measuring frequency of thebeat note. This worked well when there was an entire cycle of the beatnote inside the time window of interest.

For typical applications of radar (vehicle collision avoidance; tanklevel monitoring for large, open, non-metallic tanks; presence detectionfor security or lighting control; automatic door opening) operating inthe above restricted frequency bands, the beat note is stillsufficiently high enough in frequency for targets beyond about the 2meter range. Therefore with the traditional FFT technique, it ispossible to reliably detect targets beyond about the 2 meter range.

Other use cases require detection and distance measurements of targetswithin the near field (less than about 2 meters) of the radar sensingsystem. These use cases include tank level monitoring for small, openair tanks; collision avoidance for objects within inches of each other;location of in-wall objects (pipes, conduit, studs), gesture detection;and others.

Near field determinations of distance ranging and speed determinationhave been attempted and suffer from inaccuracies the shorter the nearfield. What is needed is improved accuracy in radar systems especiallyin near field applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The present inventions are illustrated by way of example and are notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

The details of the preferred embodiments will be more readily understoodfrom the following detailed description when read in conjunction withthe accompanying drawings wherein:

FIG. 1 illustrates a schematic block diagram of a radar apparatus withquiet switch calibration according to embodiments of the presentinventions;

FIG. 2 illustrates a schematic block diagram of a receive path accordingto an exemplary embodiment of the present inventions;

FIG. 3 illustrates a plot of a sweep signal according to an exemplaryembodiment of the present inventions;

FIG. 4 illustrates a plot of a varying frequency signal according to anexemplary embodiment of the present inventions;

FIG. 5 illustrates a plot of a received signal according to embodimentsof the present inventions;

FIG. 6 illustrates a plot of a previously stored compensation signalaccording to embodiments of the present inventions;

FIG. 7 illustrates a plot of a compensated received signal according toembodiments of the present inventions;

FIG. 8 illustrates a plot of a frequency spectrum signal of an exemplarypreferred embodiment of the radar apparatus, when the previously storedcompensation signal is essentially zero, and there is no compensation;

FIG. 9 illustrates a plot of a frequency spectrum signal according toembodiments of the present inventions;

FIG. 10 illustrates a schematic block diagram of a radar apparatusaccording to embodiments of the present inventions, during a calibrationmode;

FIG. 11 illustrates a schematic block diagram of a radar apparatusaccording to embodiments of the present inventions during a calibrationmode using a load for a quiet environment;

FIG. 12 illustrates a multi-dimensional memory for the compensationsignal memory according to embodiments of the present inventions;

FIG. 13 illustrates a schematic block diagram of a radar apparatusaccording to embodiments of the present inventions during an operationmode whereby a previously stored compensation signal may be adjusted;

FIG. 14 illustrates a schematic block diagram of a quadrature receivepath of the radar apparatus according to embodiments of the presentinventions;

FIG. 15 illustrates a plot of an in-phase received signal according toembodiments of the present inventions;

FIG. 16 illustrates a plot of a quadrature received signal according toembodiments of the present inventions;

FIG. 17 illustrates a plot of a previously stored in-phase compensationsignal according to embodiments of the present inventions;

FIG. 18 illustrates a plot of a previously stored quadraturecompensation signal according to embodiments of the present inventions;

FIG. 19 illustrates a plot of an in-phase compensated received signalaccording to embodiments of the present inventions;

FIG. 20 illustrates a plot of a quadrature compensated received signalaccording to embodiments of the present inventions;

FIG. 21 illustrates a flowchart of the calibration and calibrationadjustments for an exemplary radar apparatus according to embodiments ofthe present inventions; and

FIG. 22 illustrates a flowchart of the operation for an exemplary radarapparatus according to embodiments of the present inventions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For near field targets, because the beat note frequency is low enough tobe masked by other factors, distance measurement techniques fortraditional radar sensing systems using Frequency Modulated ContinuousWave (FMCW) are inaccurate.

One of the main factors confounding the detection of near-field objectsis the frequency modulation of the carrier signal. This modulationintroduces its own signal at a frequency similar to that of the beatnote, making it difficult to distinguish the actual beat note with thetraditional Fast Fourier Transform (FFT) algorithm. Another confoundingfactor is leakage and other artifacts generated by the radar unititself.

The accuracy of distance measurements are traditionally improved bysweeping a wide bandwidth of the operating frequency of the radarsensing system, e.g. 600 MHz to 1 GHz bandwidth. This method can beutilized by enclosed environments but cannot be used for open airsystems due to the above mentioned regulatory restrictions.

Therefore, a need exists for near field object detection andcorresponding distance measurement for open air environment use cases.The challenges of near field object detection using FMCW can be overcomeby the signal processing methods and corresponding calibration techniqueas described.

Although it was understood that the beat note could not extend beyondspecific range, the present inventions have gone beyond the acceptedlimits and have achieved better results especially at a certainfrequency relationship.

It has been discovered that accuracy of measurements of characteristicsof objects measured by a radar system can be improved, by calibrationthat eliminates the ambient artifacts, especially in near fieldapplications. It has been recognized that these so called ambientartifacts particularly affect the closest in near field measurements.This is particularly a problem when using a Fast Fourier Transform (FFT)prior to peak detection for signal analysis to measure thecharacteristics of an object. It has been identified that these socalled ambient artifacts created errant peaks at low frequencies. Ifthese low frequency peaks are merely ignored, then very near fieldmeasurements become impossible. Applicants propose approaches foreliminating these errant low frequency peaks and thereby achievingbetter accuracy in radar measurements systems, especially as the fielddistance shortens.

FIG. 1 illustrates a schematic block diagram of a radar apparatus withquiet switch calibration according to embodiments of the presentinventions. The radar apparatus 100 measures characteristics of at leastone object 105. A distance to the object 105 is one examplecharacteristic to be measured though the characteristics measured caninclude any of presence, distance, speed, acceleration, direction ofmotion, size, and reflectivity alone or in combination. A frequencymodulated oscillator 110 generates a varying frequency signal 330 basedon a sweep signal in the embodiment illustrated in FIG. 1. A rampgenerator 120 is coupled to the frequency modulated oscillator 110 andgenerates a sweep signal 310. The frequency modulated oscillator 110 ismodulated by the sweep signal 310 to generate a varying frequency signal330. A transmitter 130 is coupled to the frequency modulated oscillator110 to generate a radar signal 135 using the varying frequency signal330. A transmit antenna 132 is coupled to the transmitter 130.

In one preferred embodiment according to that illustrated in FIG. 1, theradar apparatus 100 is a Frequency Modulated Continuous Wave (FMCW)radar apparatus. To achieve FMCW, the ramp generator 120 generates asweep signal 310 of a ramp shape that periodically repeats over time ina predetermined ramp pattern. Then the frequency modulated oscillator110 and the transmitter 130 generate the varying frequency signal 330and radar signal 135 over time based on the sweep signal 310. In theillustrated embodiment of FIG. 1 the sweep signal 310 is preferably asawtooth waveform. Alternately, besides a sawtooth waveform, thewaveform of the sweep signal 310 can take different forms such as atriangular waveform and asymmetrical variants thereof.

A receiver 140 receives a reflected radar signal 136 reflected off of anobject 105 via a receive antenna 142. The transmit antenna 132 and thereceive antenna 142 can be patch antennas of 8-elements or other numbersof elements, e.g. 2, 4, 16, or other antenna types such as horn orarray.

The receiver 140 is coupled to a receive antenna 142. The receiver 140is coupled to the same frequency modulated oscillator 110 to obtain thereflected radar signal 136 using the same varying frequency signal 330.The output of the receiver 140 produces a received signal 210.

A compensation circuit 150 is coupled to the receiver 140 to compensatethe received signal 210 based on a previously stored compensation signal165 in a memory 160 to produce a compensated received signal 220. Thecompensation circuit 150 preferably subtracts the previously storedcompensation signal 165 from the received signal 210.

The previously stored compensation signal 165 is a previously measuredreceived signal in the absence of a reflected radar signal 136. Thepreviously stored compensation signal 165 is a time domain signal in thepreferred embodiment. The previously stored compensation signal 165 ismeasured previously and representative of at least the varying frequencysignal based on the sweep signal. The previously stored compensationsignal 165 is substantially composed of undesired signals includingleakage artifacts involving one or more of the ramp generator 120including the sweep signal 310, the oscillator 110, the transmitter 130,the receiver 140, and signal couplings therebetween. Ideally thepreviously stored compensation signal 165 would be entirely composed ofjust the undesired signals including leakage artifacts, but a faintradar signal 135 may still be there because perfect absorption orquieting is nearly impossible.

The calibration mode is conducted in a quiet room environment or otherquiet environment when all radar signals were absorbed in order tomeasure and determine the previously stored compensation signal 165. Thepreviously stored compensation signal 165 is unique to a particularhardware and its prior measured characteristics due to hardwarecomponent variations and/or other factors. Nevertheless, in alternativeimplementations, depending on the consistency of different hardware andrequired performance, a same previously stored compensation signal 165can be used across multiple hardware units.

A quiet switch 191 can be used to create a quiet environment for initialcalibration. During a calibration mode, the content of the compensationsignal memory 160 is initialized or written in the exemplary embodimentof FIG. 1 in a quiet environment created by an absorptive material orthe quiet switch 191 or both. The quiet switch 191 is coupled to thetransmitter 130 or the receiver 140 or both and controls a dummy load ora termination load or both associated with one or the other or both toabsorb the radar signal 135 or the reflected radar signal 136 or both.During calibration mode, the received signal 210 is the compensationsignal 163, and is initially stored to the compensation signal memory160 from the receiver 140. During operating mode, the previously storedcompensation signal 163 is subsequently retrieved from the memory 160.When “quieting” the reflected radar signal 136, either the receipt ofthe reflected radar signal 136 can be terminated in a termination loador the transmission of the radar signal 135 can be absorbed in a dummyload.

The quiet switch 191 can be used to create a quiet environment duringoperation for an update calibration. During operation, after initialcalibration, the quiet switch 191 can be used to detect adjustmentsneeded to the previously stored compensation signal 165 in thecompensation signal memory 160. During operation mode, after initialcompensation, a secondary compensation mode can be enabled, theenvironment quieted, and the received signal 210 used to determine anadjustment to the compensation signal 163.

The previously stored compensation signal 165 in alternativeconstructions can be dependent upon various parameter values of theradar apparatus including receive gain, frequency, transmit power,sampling rate, bandwidth, and ramp time. One option is to controldifferent parts or all parts of the radar apparatus under variousparameter conditions to store different calibration measurements andlater read them for compensation based on the operation conditions.Therefore, in the preferred embodiment, multiple compensation signalsare measured and stored based on multiple sets of the various parametervalues while operating in calibration mode. The previously storedcompensation signal 165 in alternative constructions can use a lookuptable with possibly multiple dimensions based on the multiple sets ofthe various parameter values while operating in the calibration mode.The previously stored compensation signal 165 used by the compensationcircuit 150 can be chosen from a plurality of previously storedcompensation signals, each of the plurality of previously storedcompensation signals corresponding to various parameters includingreceive gain, frequency, transmit power, sampling rate, bandwidth, andramp time.

A frequency transformation circuit 170 is coupled to the compensationcircuit 150 to receive the compensated received signal 220 and produce afrequency spectrum signal 230. In the one embodiment of FIG. 1, a FastFourier Transform (FFT) is performed on the compensated received signal220 in the frequency transformation circuit 170. The frequencytransformation circuit 170 transforms the compensated received signalinto a frequency domain to produce the frequency spectrum signal 230which is representative of the compensated received signal.

Measurement of a distance characteristic for radar operating in FMCWmode can be defined by Equation 1. The relationship between distance tothe object and various system parameters is as follows:

$\begin{matrix}{R = \frac{c*{Tr}*{Fb}}{2*B\; W}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

where:R=measurable distance characteristic 185 of the object 105c=constant velocity of lightTr=time for one ramp (up chirp or down chirp) of the sweep signal 310Fb=difference in frequency of the radar signal 135 transmitted and thereflected radar signal 136 (beat frequency, a.k.a., frequency of a peakin the frequency spectrum signal 230)BW=sweep bandwidth of the varying frequency signal 330

As stated in Equation 1, distance (R) to the object 105 is a function oframp time (Tr) of the sweep signal 310 to the difference in frequency(Fb) of the radar signal 135 and the reflected radar signal 136 and thesweep bandwidth (BW) of the varying frequency signal 330. A beatfrequency or frequency of a peak in the frequency spectrum signal 230 isthe difference in frequency (Fb) of the radar signal 135 and thereflected radar signal 136. Furthermore, the resolution of distance tothe object directly depends on the measured accuracy of the differencefrequency (Fb) of the radar signal 135 and the reflected radar signal136, also known as the beat frequency. When a measured object is notfixed and moves some, the beat frequency (Fb) moves as the object moves.

Also note time and frequency have a reciprocal relationship defined byEquation 2 as follows:

$\begin{matrix}{{Tr} = \frac{1}{Fr}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

where Fr is the corresponding ramp (chirp) frequency of the sweep signal310.

In a special case where the difference in frequency of the radar signal135 and the reflected radar signal 136 (Fb) approaches the value of theramp frequency (Fr), the terms Fb and Fr can be mathematically assumedto be equal and cancel, so Equation 1 can be simplified to anapproximation as Equation 3. In this special case, Equation 1 reduces toEquation 3 as follows:

$\begin{matrix}{R = \frac{c}{2*B\; W}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where R is an ambiguous distance to the object 105. At the ambiguousdistance of this special case, measurement of the distance was nearlyimpossible prior to the calibration and compensation methods andapparatuses of embodiments disclosed herein.

Thus the radar apparatus 100 is capable of measuring characteristics tothe at least one object using an frequency relationship when a frequencydifference between the radar signal 135 and the reflected radar signal136 is near a frequency of the sweep signal 310. This frequencyrelationship exists for distance and other characteristics such asvelocity. Measurements of characteristics taken near this frequencyrelationship could not previously be resolved or were inaccurate.

The relation of Equation 3 simply states that an ambiguous distance (R)to the object 105 is inversely related to the sweep bandwidth (BW) ofthe radar signal 135. When measuring a characteristic other than theexample of distance, such as velocity, an ambiguous point can berecognized by a velocity equation different than Equation 3, but onewhere the ramp frequency (Fr) becomes equal to the difference infrequency of the radar signal 135 and the reflected radar signal 136(Fb). Prior to the calibration and compensation methods and apparatusesof embodiments disclosed herein, radar was incapable of measuringcharacteristics of objects when the ramp frequency (Fr) was near thedifference in frequency of the radar signal 135 and the reflected radarsignal 136 (Fb). When the ramp frequency (Fr) was near the difference infrequency of the radar signal 135 and the reflected radar signal 136(Fb), the frequency spectrum domain peaks were too close together toresolve. Thus, the radar apparatus 100 measures characteristics ofobjects even when the ramp frequency (Fr) is near the difference infrequency of the radar signal 135 and the reflected radar signal 136(Fb).

Noteworthy is also the fact that there are physical as well asregulatory limits on the bandwidth BW term. This also highlights thefact that when Fr=Fb in the time domain, one cycle of the differencefrequency fits exactly during one ramp or chirp. Furthermore, othervariations of this case exist when the beat frequency (Fb) is closer toFr in such a way that the beat frequency (Fb) may be slightly lower thanthe ramp frequency (Fr).

Accurate determination of a measurable distance characteristic isfurther compromised by the leakage of the radar signal within the radarcircuitry that presents the leakage responses together with the desiredbeat frequency (Fb). To accurately measure beat frequency (Fb), normalfrequency transformation methods such as FFT become exceedinglydifficult to resolve these small frequency differences. The peaks in theFFT frequency plot become either so close together or so broad that apeak detector is unable to uniquely identify the peak due to the beatfrequency (Fb). This range of operation when the desired beat frequency(Fb) is lower than the ramp frequency (Fr) can be defined as the nearfield.

FIG. 2 illustrates a schematic block diagram of one preferred embodimentof a receive path including a receiver 140. The low noise amplifier(LNA) 144 is coupled to the receiver antenna 142 and amplifies thereflected radar signal 136 received at the receiver antenna. Thereceiver 140 uses a mixer 145 to mix the amplified reflected radarsignal with the varying frequency signal 330 in the one preferredembodiment according to that illustrated in FIG. 2. The receiver 140 canuse a demodulator or analog to digital converter 148 at its output orthe demodulator or analog to digital converter 148 can be implementedseparate from the receiver. Additionally filtering can occur in thereceiver 140 associated with the demodulator or analog to digitalconverter 148. A high pass filter 141 as illustrated helps remove theleakage artifacts. The output of the receiver 140 and the subsequentdemodulator or analog to digital converter produces a received signal210.

In the one embodiment of FIG. 2, an amplifier 172 is coupled between thecompensation circuit 150 and the frequency transformation circuit 170 toamplify the compensated received signal 220 to improve signal to noiseratio and consequently peak detection by the peak detector 180.

A peak detector 180 is coupled to the frequency transformation circuit170 and determines a signal or peak representative of a characteristic185 of the object 105 which the reflected radar signal 136 was reflectedbased on at least one peak of the frequency spectrum signal 230. Thepeak detector 180 can recognize either one maximum peak or multiplepeaks and not necessarily a maximum peak. The peak detector 180 canrecognize multiple characteristics of an object 105 or a characteristicof multiple objects depending on how many peaks the detection isdesigned to detect. Examples of characteristics measured by the radarapparatus include a distance to the object 105 as well as any ofpresence, speed, acceleration, direction of motion, size, andreflectivity alone or in combination. One or more peak detectionsindicate these characteristics. Additionally, the peaks at an up or downchirp of the sweep signal will provide more information for indicatingthese characteristics. When the compensation signal memory 160 storesdifferent values for up and down chirp compensation parameters, accuracyis improved.

An offset correction circuit 186 is coupled to the peak detector 180 toapply a singular dimension offset to the signal representative of thecharacteristic 185 to produce a signal representative of an offsetcorrected characteristic 187. The singular dimension offset applied inone embodiment can be a distance. In other embodiments it can be othervalues such as presence, speed, acceleration, direction of motion, size,and reflectivity or combinations. The offset correction is also notalways needed and may be zero or not implemented depending on theapplication or environment of the radar apparatus.

FIG. 3 illustrates a sweep signal 310 in an exemplary embodiment of thepresent inventions. The sweep signal 310 varies in amplitude over timeand is of a ramp shape that periodically repeats over time in apredetermined ramp pattern, according to the preferred embodiment. Thehorizontal axis is in units of time in milliseconds (ms). The verticalaxis is the amplitude of the sweep signal. The example plot in FIG. 3 isfor illustrative purposes. The range of frequencies, the time period,and the pattern of the sweep signal 310 may vary depending upon therequirements of an embodiment of the radar apparatus 100.

FIG. 4 illustrates a varying frequency signal 330. The varying frequencysweep signal is a frequency modulated continuous wave (FMCW) signal, inan exemplary preferred embodiment, where the continuous wave is asinewave and the frequency modulation is according to the sweep signal310. The horizontal axis is in units of time in milliseconds (ms). Thevertical axis is the normalized amplitude of the signal. The exampleplot in FIG. 4 is for illustrative purposes and has been drawn not toscale to more readily show a reduced number of individual cycles. Thecharacteristics of the varying frequency signal 330 may vary dependingupon the requirements of an embodiment of the radar apparatus 100.

FIG. 5 illustrates a received signal 210, of an exemplary preferredembodiment of the radar apparatus 100. The horizontal axis is in unitsof time in milliseconds (ms). The vertical axis is the amplitude of thereceived signal. The example plot in FIG. 5 is for illustrativepurposes. Characteristics of the received signal 210 may vary dependingupon the embodiment of the radar apparatus 100, the settings of theparameter values of the radar apparatus, the operating environment, andother factors.

FIG. 6 illustrates an exemplary previously stored compensation signal165, of an exemplary preferred embodiment of the radar apparatus 100.The horizontal axis is in units of time in milliseconds (ms). Thevertical axis is the amplitude of the previously stored compensationsignal. The example plot in FIG. 6 is for illustrative purposes. Thecharacteristics of the previously stored compensation signal 165 mayvary depending upon the embodiment of the radar apparatus 100. Thecharacteristics of the previously stored compensation signal 165 mayalso vary depending upon the settings of the parameter values of theradar apparatus when the previously stored compensation signal wasmeasured and stored, and other factors.

FIG. 7 illustrates a compensated received signal 220, of an exemplarypreferred embodiment of the radar apparatus 100. The horizontal axis isin units of time in milliseconds (ms). The vertical axis is theamplitude of the compensated received signal. The compensated receivedsignal illustrated in FIG. 7 is the output result of the compensationcircuit 150, with the inputs of the received signal 210 as illustratedin FIG. 5 and of the previously stored compensation signal 165 asillustrated in FIG. 6. The example plot in FIG. 7 is for illustrativepurposes. The characteristics of the compensated received signal 220 mayvary depending upon the embodiment of the radar apparatus 100. Thecharacteristics of the compensated received signal 220 may also varydepending upon the settings of the parameter values of the radarapparatus, the operating environment, and other factors.

FIG. 8 illustrates a frequency spectrum signal of an exemplary preferredembodiment of the radar apparatus 100, when the previously storedcompensation signal is essentially zero, and there is no compensation.The horizontal axis is in units of frequency in Hertz (Hz). The verticalaxis is the amplitude of the frequency spectrum plot. The previouslystored compensation signal may be zero if the calibration of the radarapparatus has not been conducted, if an indicator within the radarapparatus has a status of the calibration not being conducted yet, ifthe previously stored compensation signal has not been stored intomemory yet, or if similar pre-calibration states or conditions are setwithin the radar apparatus. The frequency spectrum signal of thereceived signal of FIG. 8 is for illustrative and comparison purposes.

FIG. 9 illustrates a frequency spectrum signal 230, of an exemplarypreferred embodiment of the radar apparatus 100. The horizontal axis isin units of frequency in Hertz (Hz). The vertical axis is the amplitudeof the frequency spectrum plot. The illustrated frequency spectrumsignal in this FIG. 8 is the output result of the exemplary Fast Fouriertransform (FFT) by the frequency transformation circuit, with the inputof the compensated received signal 220 as illustrated in FIG. 7. Theexample plot in FIG. 9 is for illustrative purposes. The characteristicsof the frequency spectrum signal 230 may vary depending upon theembodiment of the radar apparatus 100. The characteristics of thefrequency spectrum signal 230 may also vary depending upon the settingsof the parameter values of the radar apparatus, the operatingenvironment, and other factors.

When comparing FIG. 8 and FIG. 9, it is evident that the peaks of thefrequency spectrum signal are dramatically different, especially atfrequencies below about 800 Hz. The highest peak of FIG. 8, occurring at117 Hz, corresponds to the ramp frequency of the sweep signal 310. Whenthe peak detector 180 analyzes the frequency spectrum signal of FIG. 8,the peak detector will falsely detect an object at a distancecorresponding to the ramp frequency. When the peak detector 180 analyzesthe frequency spectrum signal of FIG. 9, the peak detector willcorrectly detect an object at a distance corresponding to the peakfrequency occurring at 384 Hz. The invention not only minimizes theeffect of the ramp frequency in the compensated frequency spectrumsignal, but the invention also adjusts the frequency spectrum signal toimprove the accuracy of measuring characteristics of the at least oneobject. In the illustrated frequency spectrum signal withoutcompensation of FIG. 8, the detected object has a corresponding peak at331 Hz. In the illustrated compensated frequency spectrum signal of FIG.9, the frequency peak of the detected object is adjusted to 384 Hz,which corresponds to a more accurate measurement of the object, per thecorresponding conditions.

FIG. 10 illustrates a schematic block diagram of a radar apparatusaccording to embodiments of the present inventions during a calibrationmode. In the calibration mode, the content of the compensation signalmemory 160 is initialized or written. In the embodiment, the radarapparatus 100 is placed within an absorbent empty room 710 whereinessentially the entire radar signal 135 is absorbed. Alternately thisroom can be an open air range. A mode switch 720 is coupled to thereceived signal 210 and the compensation signal memory 160. An externalcontrol interface 730 controls the mode switch to switch from thecompensation circuit 150, for normal operating mode, to the compensationsignal memory 160, for calibration mode. The external control interface730 can be a button control by a user of the radar apparatus 100 orcontrol of the radar apparatus 100 in a factory environment by amicroprocessor internal or external to the radar apparatus 100. Duringcalibration mode, the compensation signal 163 is the received signal210, is stored to the compensation signal memory 160, and issubsequently retrieved from the memory 160 as the previously storedcompensation signal during normal operating mode. The compensationcircuit 150, the frequency transformation circuit 170 and the peakdetector 180 are present but are not necessarily active duringcalibration mode. Even when not present, the purpose of the calibrationis to enable their subsequent accurate use.

FIG. 11 illustrates an alternative schematic block diagram of a radarapparatus according to embodiments of the present inventions during acalibration mode using a load for a quiet environment. In thealternative embodiments of FIG. 11, the radar apparatus 100 need notnecessarily be placed within an absorbent empty room. A mode switch 720is coupled to the received signal 210 and the compensation signal memory160. A single pole double throw load switch 192 is coupled to thetransmitter 130 and a dummy load 194 to send and absorb the radar signal135 into the dummy load 194. The receiver 140 is connected to eitherantenna 142 or to termination load 196 via a double pole double throwtermination switch 193. The antenna 142 is connected to either receiver140 or to termination load 197 via switch 193. An external controlinterface 730 controls the mode switch 720, the load switch 192, and thedouble pole double throw termination switch 193. The external controlinterface 730 can be a button control by a user of the radar apparatus100 or control of the radar apparatus 100 in a factory environment by amicroprocessor internal or external to the radar apparatus 100. Forcalibration mode, the external control interface controls the modeswitch to switch to the compensation signal memory 160. Additionally,for calibration mode, the external control interface 730 controls wheneach of the load switch 192 and the double pole double throw terminationswitch 193 respectively couples the transmitter 130 to the dummy load194 and the receiver 140 to the termination load 196 and antenna 142 totermination load 197. Besides an embodiment with both termination loads196 and 197, in a first alternative embodiment, the double pole doublethrow termination switch 193 can be a single pole double throw switchand the termination load 197 omitted, or in a second alternativeembodiment, the double pole double throw termination switch 193 can be asingle pole double throw switch and the termination load 196 omitted.The coupling may be activated individually for either the load switch192 or the double pole double throw termination switch 193.Alternatively, the coupling may be activated for both the load switch192 and the double pole double throw termination switch 193 at the sametime. During calibration mode, the received signal 210 is thecompensation signal 163, is stored to the compensation signal memory160, and is subsequently retrieved from the memory 160 as the previouslystored compensation signal during normal operating mode. Thecompensation circuit 150, the frequency transformation circuit 170 andthe peak detector 180 are present but are not necessarily active duringcalibration mode.

Alternatively, in calibration mode, the radar apparatus 100 may beplaced within an absorbent empty room 710, as illustrated in FIG. 10;and the external control interface 730 may control at least one of theload switch and the termination switch to switch to the dummy load 194and the termination loads 196 and 197, respectively, as illustrated inFIG. 11. The external control interface controls the mode switch toswitch to the compensation signal memory 160. During calibration mode,the received signal 210 is the compensation signal 163, is stored to thecompensation signal memory 160, and is subsequently retrieved from thememory 160 as the previously stored compensation signal during normaloperating mode.

FIG. 12 illustrates a multi-dimensional memory for the compensationsignal memory according to embodiments of the present inventions. FIG.12 illustrates a multi-dimensional memory 250 for the compensationsignal memory 160 storing values of transmit power, received gain, ramptime, and sweep bandwidth, among others for the previously storedcompensation signal 165. In the embodiment of FIG. 12, each cell of themulti-dimensional memory 250 contains stored values of amplitude overtime when exercised according to corresponding parameter settings. TheX-axis (going towards the right of the page of the multi-dimensionalmemory 250) shows two example ramp time settings 251 of many possiblevalues for a ramp time settings 251 of the sweep signal 310. (In theexample embodiment of FIG. 1, the ramp time is the time period the sweepsignal 310 goes from the lowest frequency of the varying frequencysignal 330 to the highest frequency of the varying frequency signal330.) The Y-axis (going towards the left of the page of themulti-dimensional memory 250), shows two example gain settings 252 ofmany possible values for receiver gain settings 252 for the receiver140. The Z-axis (going towards the top of the page of themulti-dimensional memory 250) shows two examples of transmit powersettings 253 among many possible transmit power settings 253 for thetransmitter 130. In calibration mode, a quieted receiver 140 writes toeach cell of the multi-dimensional memory 250 a compensation signal 165corresponding to its combination of settings. In calibration mode, eachcombination of these settings is exercised to write and fill themulti-dimensional memory 250. Then, in operation mode, the calibrationcircuit 150 reads a previously stored compensation signal 165 from acell of the multi-dimensional memory 250 corresponding to itscombination of settings needed for operation.

FIG. 13 illustrates a schematic block diagram of a radar apparatusaccording to embodiments of the present inventions during an operationmode whereby the previously stored compensation signal 165 may beadjusted. A load switch 192 is coupled to the transmitter 130 and adummy load 194 to send and absorb the radar signal 135 into the dummyload 194. The compensation signal adjustment circuit 650 adjusts thepreviously stored compensation signal 165 based on a measurement of thereceived signal when the load switch 192 terminates the radar signal 135into the dummy load 194. The adjustment to the previously storedcompensation signal 165 is based on a difference between a currentmeasurement of the received signal when the load switch 192 terminatesthe radar signal 135 into the dummy load and a previously storedcompensation signal 165 residing within the compensation signal memory160, which was captured in a quiet environment when all transmit signalswere absorbed.

A termination switch 193 is coupled to the receiver 140 and atermination loads 196 and 197 to quiet the reflected radar signal 136.The reflected radar signal is quieted by switching the receiver from thereceive antenna 142 to the termination load 196 and the receive antenna142 to termination load 197. The compensation signal adjustment circuit650 adjusts the previously stored compensation signal 165 based on ameasurement of the received signal when the termination switch 193 isswitched to the termination load 196. The adjustment to the previouslystored compensation signal 165 is based on a difference between acurrent measurement of the received signal when the termination switch193 quiets the reflected radar signal 136 and a previously storedcompensation signal 165 residing within the compensation signal memory160, which was captured in a quiet environment when all reflected radarsignals were quieted.

The external control interface 730 can be a button control by a user ofthe radar apparatus 100 or control of the radar apparatus 100 in afactory environment by a microprocessor internal or external to theradar apparatus 100. The external control interface 730 controls wheneach of the load switch 192 and the termination switch 193 respectivelycouples the transmitter 130 to the dummy load 194 and the receiver 140to the termination load 196. The coupling may be activated individuallyfor either the load switch 192 or the termination switch 193.Alternatively, the coupling may be activated for both the load switch192 and the termination switch 193 at the same time.

FIG. 14 illustrates a schematic block diagram of one exemplary preferredembodiment of a quadrature receive path of the radar apparatus 100. Areceiver 440 receives a reflected radar signal 136 reflected off of anobject 105 via a receive antenna 142. The receiver 440 is coupled to areceive antenna 142. The low noise amplifier (LNA) 144 is coupled to thereceive antenna 142 and amplifies the reflected radar signal 136received at the receive antenna. The receiver 440 is coupled to thefrequency modulated oscillator 110. The receiver 440 uses an in-phasemixer 146 and a quadrature mixer 147 to mix the amplified reflectedradar signal with the varying frequency signal 330 in the one preferredembodiment, according to that illustrated in FIG. 14. The in-phase mixer146 is coupled to an in-phase demodulator and analog-to-digitalconverter (A/D) 143. The quadrature mixer 147 is coupled to a quadraturedemodulator and analog-to-digital converter (A/D) 149. One output of thereceiver 440 and the subsequent in-phase demodulator A/D 143 produces anin-phase received signal 511. A second output of the receiver 140 andthe subsequent quadrature demodulator A/D 149 produces a quadraturereceived signal 512.

An in-phase compensation circuit 551 is coupled to the receiver 440, andmore specifically coupled to the in-phase demodulator A/D 143, tocompensate the in-phase received signal 511 based on a previously storedin-phase compensation signal 166 in a memory 161 to produce an in-phasecompensated received signal 521. A quadrature compensation circuit 552is coupled to the receiver 140, and more specifically coupled to thequadrature demodulator A/D 149, to compensate the quadrature receivedsignal 512 based on a previously stored quadrature compensation signal167 in a memory 162 to produce a quadrature compensated received signal522.

The previously stored in-phase compensation signal 166 and thepreviously stored quadrature compensation signal 167 are previouslymeasured in-phase received signal and previously measured quadraturereceived signal, respectively, in the absence of a reflected radarsignal 136, measured during a calibration mode. The previously storedin-phase compensation signal 166 and the previously stored quadraturecompensation signal 167 are time domain signals in the preferredembodiment. The previously stored in-phase compensation signal 166 andpreviously stored quadrature compensation signal 167 are measuredpreviously and representative of at least the varying frequency signalbased on the sweep signal. The previously stored in-phase compensationsignal 166 and the previously stored quadrature compensation signal 167are composed of undesired signals including leakage artifacts involvingone or more of the ramp generator 120 including the sweep signal 310,the oscillator 110, the transmitter 130, the receiver 140, and signalcouplings therebetween. The previously stored in-phase compensationsignal 166 and the previously stored quadrature compensation signal 167are dependent upon various parameter values of the radar apparatusincluding receive gain, frequency, transmit power, sampling rate,bandwidth, and ramp time. Therefore, in the preferred embodiment,multiple compensation signals are measured and stored based on multiplesets of the various parameter values while operating in calibrationmode. The calibration mode is conducted in a quiet room environment orother quiet environment when all radar signals were absorbed in order tomeasure and determine the previously stored in-phase compensation signal166 and the previously stored quadrature compensation signal 167. Thepreviously stored in-phase compensation signal 166 and the previouslystored quadrature compensation signal 167 comprise a lookup table withpossibly multiple dimensions based on the multiple sets of the variousparameter values while operating in the calibration mode. The previouslystored in-phase compensation signal 166 and the previously storedquadrature compensation signal 167 may be unique to a particularhardware and its prior measured characteristics due to hardwarecomponent variations and/or other factors.

The previously stored in-phase compensation signal 166 and thepreviously stored quadrature compensation signal 167 respectively usedby the in-phase compensation circuit 551 and the quadrature compensationcircuit 552 can be chosen from a plurality of previously storedcompensation signals, each of the plurality of previously storedcompensation signals corresponding to various parameters includingreceive gain, frequency, transmit power, sampling rate, bandwidth, andramp time.

The in-phase compensation circuit 551 preferably subtracts thepreviously stored in-phase compensation signal 166 from the in-phasereceived signal 511 to generate the in-phase compensated received signal521. The quadrature compensation circuit 552 preferably subtracts thepreviously stored quadrature compensation signal 167 from the quadraturereceived signal 512 to generate the quadrature compensated receivedsignal 522.

A complex-number frequency transformation circuit 470 is coupled to thein-phase compensation circuit 551 and the quadrature compensationcircuit 552 to receive the in-phase compensated received signal 521 andthe quadrature compensated received signal 522 and produce a frequencyspectrum signal 230. In the one embodiment of FIG. 14, a Fast FourierTransform (FFT) is performed on complex compensated received signalsfrom the complex-number frequency transformation circuit 470. Thesecomplex compensated received signals are the in-phase compensatedreceived signal 521 and the quadrature compensated received signal 522.The complex-number frequency transformation circuit 470 transforms thecompensated received signal into the frequency domain to producefrequency spectrum signal 230 which is representative of the compensatedreceived signal. The frequency spectrum signal 230 is illustrated inFIG. 9.

A peak detector 180 and offset correction circuit 186 may furtherprocess and analyze the frequency spectrum signal 230, as illustrated inFIG. 1 and as previously described.

Two amplifiers, which may be coupled between respective of the in-phasecompensation circuit 551 and the complex-number frequency transformationcircuit 470 and coupled between the quadrature compensation circuit 552and the complex-number frequency transformation circuit 470, may furtheramplify the in-phase compensated received signal 521 and the quadraturecompensated received signal 522 to improve signal to noise ratio andconsequently peak detection by a peak detector 180, as illustrated inFIG. 2 and as previously described.

FIG. 15 illustrates an in-phase received signal 511, of an exemplarypreferred embodiment of the radar apparatus 100. The horizontal axis isin units of time in milliseconds (ms). The vertical axis is theamplitude of the received signal. The example plot in FIG. 15 is forillustrative purposes. The characteristics of the in-phase receivedsignal 511 may vary depending upon the embodiment of the radar apparatus100. The characteristics of the in-phase received signal 511 may alsovary depending upon the settings of the parameter values of the radarapparatus, the operating environment, and other factors.

FIG. 16 illustrates a quadrature received signal 512, of an exemplarypreferred embodiment of the radar apparatus 100. The horizontal axis isin units of time in milliseconds (ms). The vertical axis is theamplitude of the received signal. The example plot in FIG. 16 is forillustrative purposes. The characteristics of the quadrature receivedsignal 512 may vary depending upon the embodiment of the radar apparatus100. The characteristics of the quadrature received signal 512 may alsovary depending upon the settings of the parameter values of the radarapparatus, the operating environment, and other factors.

FIG. 17 illustrates a previously stored in-phase compensation signal166, of an exemplary preferred embodiment of the radar apparatus 100.The horizontal axis is in units of time in milliseconds (ms). Thevertical axis is the amplitude of the previously stored in-phasecompensation signal. The example plot in FIG. 17 is for illustrativepurposes. The characteristics of the previously stored in-phasecompensation signal 166 may vary depending upon the embodiment of theradar apparatus 100. The characteristics of the previously storedin-phase compensation signal 166 may also vary depending upon thesettings of the parameter values of the radar apparatus when thepreviously stored compensation signal was measured and stored, and otherfactors.

FIG. 18 illustrates a previously stored quadrature compensation signal167, of an exemplary preferred embodiment of the radar apparatus 100.The horizontal axis is in units of time in milliseconds (ms). Thevertical axis is the amplitude of the previously stored quadraturecompensation signal. The example plot in FIG. 18 is for illustrativepurposes. The characteristics of the previously stored quadraturecompensation signal 167 may vary depending upon the embodiment of theradar apparatus 100. The characteristics of the previously storedquadrature compensation signal 167 may also vary depending upon thesettings of the parameter values of the radar apparatus when thepreviously stored compensation signal was measured and stored, and otherfactors.

FIG. 19 illustrates an in-phase compensated received signal 521, of anexemplary preferred embodiment of the radar apparatus 100. Thehorizontal axis is in units of time in milliseconds (ms). The verticalaxis is the amplitude of the in-phase compensated received signal. Theillustrated in-phase compensated received signal in this FIG. 19 is theoutput result of the in-phase compensation circuit 551, with the inputsof the in-phase received signal 511 and of the previously storedin-phase compensation signal 166, as illustrated in FIG. 14. The exampleplot in FIG. 19 is for illustrative purposes. The characteristics of thein-phase compensated received signal 521 may vary depending upon theembodiment of the radar apparatus 100. The characteristics of thein-phase compensated received signal 521 may also vary depending uponthe settings of the parameter values of the radar apparatus, theoperating environment, and other factors.

FIG. 20 illustrates a quadrature compensated received signal 522, of anexemplary preferred embodiment of the radar apparatus 100. Thehorizontal axis is in units of time in milliseconds (ms). The verticalaxis is the amplitude of the quadrature compensated received signal. Theillustrated quadrature compensated received signal in this FIG. 20 isthe output result of the quadrature compensation circuit 552, with theinputs of the quadrature received signal 512 and of the previouslystored quadrature compensation signal 167, as illustrated in FIG. 14.The example plot in FIG. 20 is for illustrative purposes. Thecharacteristics of the quadrature compensated received signal 522 mayvary depending upon the embodiment of the radar apparatus 100. Thecharacteristics of the quadrature compensated received signal 522 mayalso vary depending upon the settings of the parameter values of theradar apparatus, the operating environment, and other factors.

FIG. 21 illustrates a flowchart of the calibration and calibrationadjustments for an exemplary radar apparatus according to embodiments ofthe present inventions. The calibration flow begins at step 801 ofdeploying the radar apparatus in a quiet room environment. In step 802the transmitter and receiver of the radar apparatus are then activatedand the transmitter emits the radar signal. The quiet room environmentabsorbs essentially the entirety of the emitted radar signal.Alternatively to a quiet room environment, as illustrated in FIG. 11,the radar signal may be sent to a dummy load at the transmitter and/orthe receiver may be terminated by a termination load, to quietessentially the entirety of the radar signal. In step 803 the receivermeasures the received signal during this condition when essentially theentirety of the transmit signals are absorbed by the quiet environment.By the quiet environment, the transmit signals are sent to a dummy load,and/or the receiver is terminated by a termination load 803. In step 804the measured received signal is stored into a memory of the radarapparatus as a compensation signal indicative of undesired signalsincluding leakage artifacts. The initial calibration process ends withsaid step 804 of storing of the compensation signal into memory.

During operational mode, calibration adjustments are made in steps 805and 806. In step 805 the radar apparatus may be switched to a mode inwhich the transmit signals are sent to a dummy load and/or the receiveris terminated by a termination load whereby quieting essentially theentirety of the reflected radar signal. While in this quiet mode, thepreviously stored compensation signal may be adjusted in step 806 basedon a measurement of the received radar signal. This adjustedcompensation signal may then be used to compensate future receivedsignals during normal operational mode.

FIG. 22 illustrates a flowchart of the operation for an exemplary radarapparatus according to embodiments of the present inventions. Theoperation flow begins in step 821 with the radar apparatus deployed inan intended operating environment. In step 822 the transmitter is thenactivated to transmit a frequency modulated radar signal. The receiverreceives the reflected radar signal which is reflected off of at leastone object in step 823 and mixes the reflected radar signal with thevarying frequency signal to generate the received signal. Step 824applies the previously stored compensation signal to the received signalto create the compensated received signal. Step 825 transforms thecompensated received signal into a frequency spectrum signal. In onepreferred embodiment, a Fast Fourier Transform (FFT) performs thefrequency transformation. Step 826 identifies one or more peaks in thefrequency spectrum signal. Step 827 reports the characteristics of theat least one object based on the identified peaks in the frequencyspectrum signal. The reported characteristics may include presence,distance, speed, acceleration, direction of motion, size, andreflectivity alone or in combination.

The radar apparatus of the present inventions is useful for measuring invarious applications, including security and safety systems, traincrossings, cross roads, power tools, intruder alert, high-end lighting.It is also useful for medical application use—heart beat and/orbreathing detection. It is additionally useful to detect and resolvemultiple stationary objects. It is also additionally useful forthru-wall object detection or to detect different sizes of objectswithin a wall or automotive applications.

The signal processing techniques disclosed herein with reference to theaccompanying drawings are preferably implemented on one or more digitalsignal processors (DSPs) or other microprocessors. Nevertheless, suchtechniques could instead be implemented wholly or partially as discretecomponents or hardwired circuits. Further, it is appreciated by those ofskill in the art that certain well known digital processing techniquesare mathematically equivalent to one another and can be represented indifferent ways depending on choice of implementation.

Any letter designations such as (a) or (b) etc. used to label steps ofany of the method claims herein are step headers applied for readingconvenience and are not to be used in interpreting an order or processsequence of claimed method steps. Any method claims that recite aparticular order or process sequence will do so using the words of theirtext, not the letter designations.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

Any trademarks listed herein are the property of their respectiveowners, and reference herein to such trademarks is generally intended toindicate the source of a particular product or service.

Although the inventions have been described and illustrated in the abovedescription and drawings, it is understood that this description is byexample only, and that numerous changes and modifications can be made bythose skilled in the art without departing from the true spirit andscope of the inventions. Although the examples in the drawings depictonly example constructions and embodiments, alternate embodiments areavailable given the teachings of the present patent disclosure.

What is claimed is:
 1. A radar apparatus for measuring at least onecharacteristic of at least one object, comprising an oscillator togenerate an oscillating signal; a transmitter operatively coupled to theoscillator to amplify the oscillating signal and generate a radarsignal; a receiver operatively coupled to the oscillator to receive areflected radar signal reflected off of the at least one object andreceive the reflected radar signal to produce a received signal usingthe oscillating signal; a compensation signal memory operatively coupledto the receiver for holding a previously stored compensation signal andto write the received signal into the compensation signal memory as thepreviously stored compensation signal when operating in a calibrationmode of the radar apparatus; a compensation circuit operatively coupledto the receiver and the compensation signal memory to compensate thereceived signal based on the previously stored compensation signal toproduce a compensated received signal; a quiet switch operativelycoupled at least one of the transmitter and the receiver to quiet thereflected radar signal and determine the previously stored compensationsignal, during the calibration mode of the radar apparatus; and acharacteristic determination circuit operatively coupled to thecompensation circuit to receive the compensated received signal andmeasure the characteristic of the object which the reflected radarsignal was reflected based on the compensated received signal, during anoperation mode of the radar apparatus.
 2. A radar apparatus according toclaim 1, wherein the radar apparatus further comprises: a transmitantenna operatively coupled to the transmitter to transmit the radarsignal; and a dummy load; and wherein the quiet switch comprises a firstswitch operatively coupled to the transmitter, the dummy load and thetransmit antenna to send and absorb the radar signal into the dummy loadrather than sending the radar signal to the transmit antenna, whenoperating in a calibration mode; and a second switch operatively coupledto the receiver, the compensation circuit and the compensation signalmemory to write the received signal into the compensation signal memorywhen operating in a calibration mode.
 3. A radar apparatus according toclaim 1, wherein the radar apparatus further comprises: a terminationload; and a receive antenna operatively coupled to the receiver toreceive the reflected radar signal; and wherein the quiet switchcomprises a first switch operatively coupled to the termination load andat least one of the receiver and the receive antenna to quiet thereflected radar signal, when operating in a calibration mode; and asecond switch operatively coupled to the receiver, the compensationcircuit and the compensation signal memory to write the received signalinto the compensation signal memory when operating in a calibrationmode.
 4. A radar apparatus according to claim 3, wherein the firstswitch is operatively coupled to the termination load, the receiver, andthe receive antenna to quiet the reflected radar signal, when operatingin a calibration mode.
 5. A radar apparatus according to claim 3,wherein the first switch is operatively coupled to the termination loadand the receiver to quiet the reflected radar signal, when operating ina calibration mode.
 6. A radar apparatus according to claim 3, whereinthe first switch is operatively coupled to the termination load and thereceive antenna to quiet the reflected radar signal, when operating in acalibration mode.
 7. A radar apparatus according to claim 1, wherein theradar apparatus further comprises: a transmit antenna operativelycoupled to the transmitter to transmit the radar signal; and a dummyload; and wherein the quiet switch comprises a load switch operativelycoupled to the transmitter, the dummy load and the transmit antenna tosend and absorb the radar signal into the dummy load rather than sendingthe radar signal to the transmit antenna; and a compensation signaladjustment circuit operatively coupled between the receiver and thecompensation signal memory to adjust the previously stored compensationsignal based on a measurement of the received signal when the loadswitch terminates the radar signal into the dummy load when operating ina calibration mode.
 8. A radar apparatus according to claim 7, whereinthe adjustment to the previously stored compensation signal by thecompensation signal adjustment circuit is based on a difference betweena current measurement of the received signal when the load switchterminates the radar signal into the dummy load and a previously storedmeasurement of the received signal when the load switch terminated theradar signal into the dummy load, when operating in a calibration mode.9. A radar apparatus according to claim 1, wherein the radar apparatusfurther comprises: a termination load; and a receive antenna operativelycoupled to the receiver to receive the reflected radar signal; andwherein the quiet switch comprises a load switch operatively coupled tothe termination load and at least one of the receiver and the receiveantenna to quiet the reflected radar signal, when operating in acalibration mode; and a compensation signal adjustment circuitoperatively coupled between the receiver and the compensation signalmemory to adjust the previously stored compensation signal based on ameasurement of the received signal, when operating in a calibrationmode.
 10. A radar apparatus according to claim 9, wherein the adjustmentto the previously stored compensation signal by the compensation signaladjustment circuit is based on a difference between a currentmeasurement of the received signal when the load switch quiets thereflected radar signal and a previously stored measurement of thereceived signal when the load switch quieted the reflected radar signal,when operating in a calibration mode.
 11. A radar apparatus according toclaim 1, wherein the previously stored compensation signal written tothe compensation signal memory of a particular radar apparatus wasindividually calibrated and stored unique to that hardware of that oneradar apparatus of the compensation signal memory.
 12. A radar apparatusaccording to claim 1, wherein the radar apparatus further comprises asweep generator for generating a sweep signal; wherein the oscillator iscoupled to the sweep generator and modulated by the sweep signal togenerate a varying frequency signal as the oscillating signal; whereinthe transmitter is operatively coupled to the oscillator to amplify thevarying frequency signal and generate a radar signal; wherein thereceiver is operatively coupled to the oscillator to receive a reflectedradar signal reflected off of the at least one object and receive thereflected radar signal to produce a received signal using the varyingfrequency signal; and wherein the characteristic determination circuitcomprises: a frequency transformation circuit operatively coupled to thecompensation circuit to transform the compensated received signal into afrequency domain to produce a frequency spectrum signal of thecompensated received signal; and a peak detector operatively coupled tothe frequency transformation circuit to measure the characteristic ofthe object which the reflected radar signal was reflected based on apeak of the frequency spectrum signal.
 13. A radar apparatus accordingto claim 12, wherein the previously stored compensation signal isessentially composed of undesired signals including leakage artifactsinvolving one or more of the sweep generator including the sweep signal,the oscillator, the transmitter, the receiver, and signal couplingstherebetween.
 14. A radar apparatus according to claim 12, wherein theradar apparatus measures a characteristic of the at least one objectwhen a frequency difference between the radar signal and the reflectedradar signal is near a frequency of the sweep signal.
 15. A radarapparatus according to claim 12, wherein the characteristic of theobject from which the reflected radar signal was reflected comprises atleast a near field distance.
 16. A method of calibrating a radarapparatus, comprising the steps of: (a) deploying the radar apparatus ina quiet environment; (b) operating a transmitter and a receiver of theradar apparatus; (c) operating a quieting switch to quiet the reflectedradar signal; (d) measuring a received signal received by the receiverwhen essentially all transmit signals were quieted by operating thequiet switching of said step (c); and (e) storing in a compensationsignal memory of the radar apparatus essentially an entirety of thereceived signal.
 17. A method of calibrating according to claim 16,wherein said step (c) of operating a quieting switch to quiet thereflected radar signal further comprises the steps of: (c)(1) switchingthe radar signal from the transmitter to absorb essentially an entiretyof the radar signal; and (c)(2) adjusting the previously storedcompensation signal based on a measurement of the received signal whensaid step (c)(1) switches the radar signal to absorb essentially anentirety of the radar signal.
 18. A method of calibrating according toclaim 16, wherein said step (c) of operating a quieting switch to quietthe reflected radar signal further comprises the steps of: (c)(1)switching a termination load to quiet essentially an entirety of thereflected radar signal; and (c)(2) adjusting the previously storedcompensation signal based on a measurement of the received signal whensaid step (c)(1) switches the termination load to quiet essentially anentirety of the reflected radar signal.
 19. A method of measuring atleast one characteristics of at least one object using radar, comprisingthe steps of: (a) generating an oscillating signal; (b) transmitting aradar signal based on an amplification of the oscillating signal; (c)receiving a reflected radar signal reflected off of the at least oneobject; (d) producing a received signal by mixing the reflected radarsignal received in said step (c) and the oscillating signal generated insaid step (a); (e) holding a previously stored compensation signal in acompensation signal memory; (f) writing the received signal into thecompensation signal memory as the previously stored compensation signal,when operating in a calibration mode; (g) compensating the receivedsignal produced in said step (d) using the previously storedcompensation signal held in said step (e) to produce a compensatedreceived signal; and (h) operating a quiet switch to quiet the reflectedradar signal and determine the previously stored compensation signal,when operating in a calibration mode; and (i) measuring thecharacteristic of the object which the reflected radar signal wasreflected based on the compensated received signal, when operating in anoperation mode.
 20. A method according to claim 19, wherein said step(h) of operating a quiet switch to quiet the reflected radar signalduring calibration comprises the substep of (h)(1) sending the radarsignal to be absorbed into a dummy load rather than sending the radarsignal to a transmit antenna, when operating in a calibration mode. 21.A method according to claim 20, wherein said method further comprisesthe step of (j) adjusting the previously stored compensation signal heldin said step (e) based on a measurement of the received signal when saidstep (h)(1) sends the radar signal into the dummy load, when operatingin a calibration mode.
 22. A method according to claim 19, wherein saidstep (h) of operating a quiet switch to quiet the reflected radar signalduring calibration comprises the substep of (h)(1) quieting thereflected radar signal using a termination load, when operating in acalibration mode.
 23. A method according to claim 22, wherein saidmethod further comprises the step of (j) adjusting the previously storedcompensation signal held in said step (e) based on a measurement of thereceived signal when said step (h)(1) quiets the reflected radar signalusing the termination load, when operating in a calibration mode.
 24. Amethod according to claim 19, wherein said method further comprises thesteps of: (j) generating a sweep signal; and (k) generating a varyingfrequency signal as the oscillating signal by modulating an oscillatorby the sweep signal; and wherein said step (b) of transmitting amplifiesthe varying frequency signal and generates a radar signal; wherein saidstep (d) of producing produces a received signal using the reflectedradar signal received in said step (c) and the varying frequency signalas the oscillating signal generated in said step (a); and wherein saidstep (i) of measuring comprises the substeps of (i)(1) frequencytransforming the compensated received signal into a frequency domain toproduce a frequency spectrum signal representative of the compensatedreceived signal; and (i)(2) peak detecting the frequency spectrum signalto measure a characteristic of the at least one object.
 25. A methodaccording to claim 24, wherein said step (i)(2) of peak detectingmeasures a characteristic of the at least one object when a frequencydifference between the radar signal transmitted in said step (b) and thereflected radar signal received in said step (c) is near a frequency ofthe sweep signal generated in said step W.
 26. A method according toclaim 19, wherein said step (e) of holding the previously storedcompensation signal holds the previously stored compensation signal fora particular radar apparatus which was individually calibrated andstored unique to that hardware of that one particular radar apparatus.